1. Technical Field
This disclosure relates generally to an image forming apparatus including a recording head that ejects liquid droplets to form an image.
2. Description of the Background
One example of related-art image forming apparatuses such as printers, copiers, plotters, facsimile machines, and multifunction devices having two or more of printing, copying, plotting, and facsimile functions is an inkjet recording device employing a liquid ejection recording method. The inkjet recording device includes a recording head constituted of a liquid ejection head that ejects droplets of a recording liquid such as ink onto a sheet of recording media while the sheet is conveyed to form an image on the sheet. In a serial-type image forming apparatus, the recording head mounted on a carriage ejects ink droplets while the carriage is moving in a main scanning direction along a guide shaft to form an image on a sheet as the sheet is moved in a sub-scanning direction perpendicular to the main scanning direction.
Stable scanning movement of the carriage is essential for the serial-type image forming apparatus to improve accuracy in landing positions of ink droplets on the recording medium. In order to achieve stable scanning movement of the carriage, a traction position of the carriage to pull the carriage is set based on a weight, center of gravity, and sliding position of the carriage. There is known a serial-type image forming apparatus using bearings provided to the carriage. Each of the bearings has two sloped sides that contact the guide shaft and are arranged in an inverted V-shape relative to the long axis of the guide shaft, such that the guide shaft is stabilized by each of the bearings at two points, that is, the sloped sides. In one example of the above-described serial-type image forming apparatus, the sloped sides are angled to the vertical such that a force that prevents floating of the bearings from the guide shaft is greater than a force that causes the bearings to float during acceleration and deceleration of the carriage.
There is also known a serial-type image forming apparatus in which a head tank is installed on the carriage so that ink is supplied to the head tank from a main tank detachably attachable to the image forming apparatus through a supply tube. Although the supply tube generally extends along a direction of conveyance of the recording medium, sometimes it extends in a direction perpendicular to the direction of conveyance of the recording medium.
With regard to the liquid ejection recording method, there is a horizontal ejection method in which the recording medium is conveyed in a vertical direction or a direction slanted from the vertical direction and the recording head ejects ink droplets in a horizontal direction or a direction slanted from the horizontal direction to the sheet while moving reciprocally back and forth so as to form an image on the sheet. Specifically, in the image forming apparatus employing the horizontal ejection method, a nozzle surface of the recording head in which nozzles that eject ink droplets are formed is disposed vertically or at a slant from the vertical direction, and the recording head ejects the ink droplets horizontally or at a slant from the horizontal direction. Herein, the term “horizontal” includes an angular range up to 45° with respect to the horizontal, and the term “vertical” includes an angular range up to 45° from the vertical. It is to be noted that, in an image forming apparatus employing a vertical ejection method, the recording medium is conveyed in a horizontal direction or a direction slanted from the horizontal direction, and the recording head ejects ink droplets in a vertical direction or a direction slanted from the vertical direction to the sheet.
Because the nozzle surface of the recording head is disposed horizontally in the vertical ejection method, occurrence of yawing that swings the carriage in a horizontal plane during scanning of the carriage displaces the landing positions of the ink droplets on the recording medium. Appropriate setting of the angle of the two sloped sides in each of the bearings relative to the vertical direction can effectively reduce occurrence of yawing in the carriage.
By contrast, because the nozzle surface of the recording head is disposed vertically in the horizontal ejection method, occurrence of pitching that swings the carriage in a vertical plane during scanning of the carriage displaces the landing positions of the ink droplets on the recording medium. Similar to the vertical ejection method, pitching movement that swings the carriage in the vertical plane is increased in the horizontal ejection method when the two sloped sides in each of the bearings sandwich the guide shaft from the vertical direction. In addition, occurrence of pitching in the carriage cannot be reduced in the horizontal ejection method by simply changing an orientation of each of the two sloped sides to the horizontal direction in conformity with a change in an orientation of the nozzle surface from the horizontal direction to the vertical direction.